Comet Ison seems to have been destroyed in its encounter with the Sun.
Telescopes saw the giant ball of ice and dust disappear behind the star, but then fail to emerge as expected.
Astronomers continue to search for the object, but it is almost certain the much vaunted “Comet of the Century” has gone out with a whimper.
Despite its great size, Ison was probably torn apart in the immense heat and tidal forces so close to the Sun.
Prof Tim O’Brien, associate director of Jodrell Bank, UK, said: “The nucleus has gone very faint, which you wouldn’t expect.
“We can’t be sure – but it’s not looking good. We’ll have to keep watching.”
Ison had captivated skywatchers with its promise all year.
A “fresh” object flung in towards the inner Solar System from its home far beyond the outer planet Neptune, it was hoped it might produce a brilliant tail that would arc across the night sky, perhaps for weeks.
And, as it got closer and closer to the Sun, its ices did indeed begin to vaporise, releasing dust that shimmered in a distinctive trailing stream.
But from early on, it was clear Ison was unlikely to be spectacular; it was just not brightening in the way people had hoped.
This led scientists to fear for its survival when it eventually grazed past the star at a distance of just 1.2 million km at 18:35 GMT on Thursday.
The European and and US space agencies’ Sun-watching Soho satellite observed Ison approach, and sweep, behind the Sun, but then fail to come back around. Minutes after the comet should have reappeared, the Soho images showed nothing. Perhaps some debris, but nothing significant.
Other telescopes such as Nasa’s Solar Dynamics Observatory could detect no obvious sign, either.
Passing close to the Sun, Ison would have been subjected to temperatures up to abut 2,000C. And the immense gravity of the star would also have pulled and squeezed on the object as it tumbled end of end.
All the evidence suggests Ison’s nucleus was simply torn apart, in the same way that Comet Lovejoy – a previous hopeful in 2011 – was destroyed.
Comets will stay in the news, however. Next year, in October, Comet Siding Spring will breeze past Mars at a distance of little more than 100,000km. And then in November, the European Space Agency’s Rosetta mission will attempt to place a probe on the nucleus of Comet 67P/Churyumov-Gerasimenko.